1. Field of the Invention
The present invention relates to a microwave oven, and more specifically, to a microwave oven of a type having an antenna that rotates to diffuse the microwaves.
2. Description of the Background Art
Some of the conventional microwave ovens are provided with rotatable antennas (hereinafter referred to as a xe2x80x9crotational antennaxe2x80x9d) for diffusing and supplying the microwaves oscillated by a magnetron in a heating chamber. FIG. 9 shows a portion of a conventional microwave oven to which a rotational antenna is mounted. The microwave oven shown in FIG. 9 is of a type having the rotational antenna attached below the heating chamber. Moreover, FIG. 9 also shows a partial cross section of the microwave oven.
As shown in FIG. 9, a rotational antenna 90 is attached to a portion of a main body frame 98 of the microwave oven below a bottom surface 99 of the heating chamber.
Specifically, an antenna bearing 91 is first fitted to an antenna shaft 93 from above antenna shaft 93, and rotational antenna 90 is then fitted to the upper end of antenna shaft 93 and is fixed thereto with a nut 94. Antenna bearing 91 is fixed with a plurality of pins 92 along its periphery portion to main body frame 98. In addition, when antenna bearing 91 is fixed to main body frame 98, the lower portion of antenna shaft 93 is fitted to a motor shaft 95.
Upon fixing antenna bearing 91 to main body frame 98, pins 92 are inserted into main body frame 98. This insertion of pins 92, however, is a complicated task. As shown in FIG. 9, since rotational antenna 90 is located above antenna bearing 91, the insertion has to be done within the relatively narrow space between main body frame 98 and rotational antenna 90. In other words, a conventional microwave oven, when provided with a rotational antenna, disadvantageously required a complicated operation in mounting the rotational antenna. It is expected that the effort to facilitate the mounting operation would complicate the construction of the microwave oven itself.
Moreover, it is greatly desired that a microwave oven be formed such that it may supply microwaves in a manner that avoids uneven heating of the object to be heated. In a microwave oven, uneven heating of the object to be heated can, for instance, be eliminated by changing the radiation modes of the microwaves. It is expected, however, that the changing of the radiation modes of the microwaves would complicate the structure of a microwave oven.
The present invention was construed in view of such present conditions, and its object is to provide a microwave oven that can be easily formed while offering various advantages.
According to one aspect of the present invention, the microwave oven includes a heating chamber for accommodating a food product, a magnetron for supplying microwaves, a rotational antenna formed to allow rotation for stirring the microwaves oscillated by the magnetron, a motor for rotating the rotational antenna, and a motor shaft that serves as a rotational shaft for the motor, and is characterized in that the rotational antenna has a planar portion that extends on a plane intersecting the rotational shaft of the rotational antenna and a cylindrical portion having one end connected to the planar portion and the other end connected to the motor shaft and extending in the direction intersecting the planar portion.
According to the present invention, the rotational antenna is directly connected to the rotational shaft the motor.
In this manner, no such complicated operation as pinning down to fix the rotational antenna as described with reference to FIG. 9 is required when mounting rotational antenna 45. Thus, a microwave oven that is relatively easily formed and that facilitates the mounting of the rotational antenna can be provided.
In the microwave oven according to the present invention, the rotational antenna is provided in its planar portion with a first spacer for filling the gap between the rotational antenna and one of the wall surfaces inside the microwave oven, and the microwave oven preferably further includes a second spacer for filling the gap between the other end of the cylindrical portion and one of the wall surfaces inside the microwave oven.
In this manner, the rotational antenna is positioned between prescribed wall surfaces inside the microwave oven by the first spacer and the second spacer.
Moreover, in the microwave oven according to the present invention, the planar portion and the cylindrical portion of the rotational antenna are preferably formed integrally.
In this manner, the production of the rotational antenna can be facilitated since the operation of connecting the planar portion and the cylindrical portion is unnecessary.
According to another aspect of the present invention, the microwave oven includes a heating chamber for accommodating a food product, a magnetron for supplying microwaves, a rotational antenna formed to allow rotation for stirring the microwaves oscillated by the magnetron, a motor for rotating the rotational antenna, an antenna shaft serving as a rotational shaft for the rotational antenna, and a motor shaft that serves as a rotational shaft for the motor, and is characterized in that the rotational antenna is connected to one end of the antenna shaft, and the other end of the antenna shaft is fitted to the motor shaft such that the antenna shaft and the motor shaft overlap by a prescribed length in the direction intersecting the direction of rotation of the rotational antenna, and that the rotational antenna is provided with a spacer by which the gap between the rotational antenna and one of the wall surfaces inside the microwave oven is kept smaller than a prescribed length in the direction intersecting the direction of rotation of the rotational antenna.
According to the present invention, the rotational antenna, when rotated, is moved toward the direction intersecting the direction of rotation by a Coriolis force. When the force is of a magnitude that only moves the rotational antenna by a distance smaller than the prescribed length, the rotational antenna remains fitted to the motor. Moreover, even when the force exceeds the force of a magnitude required to move the rotational antenna by the prescribed length, the spacer collides with a wall surface inside the microwave oven so that the rotational antenna remains fitted to the motor.
In this manner, no such complicated operation for fixing the rotational antenna in advance as described with reference to FIG. 9 is required when positioning the rotational antenna. Thus, a microwave oven that is relatively easily formed and that facilitates the mounting of the rotational antenna can be provided.
In addition, in the microwave oven according to the present invention, one of the wall surfaces inside the microwave oven is a bottom surface of the heating chamber.
According to a still further aspect of the present invention, the microwave oven includes a heating chamber for accommodating a food product, a magnetron for supplying microwaves, a rotational antenna formed to allow rotation for stirring the microwaves oscillated by the magnetron, an antenna shaft being fixed to the rotational antenna and serving as a rotational shaft for the rotational antenna, and further an antenna bearing for supporting the antenna shaft, and is characterized in that the antenna bearing supports the antenna shaft such that the height of the antenna shaft changes according to the rotational angle of the rotational antenna.
According to the present invention, the rotational antenna is fixed to the antenna shaft so that the height can be changed through rotation.
Therefore, the rotational antenna can change its height simply by rotating. In addition, by changing the height of the rotational antenna, the radiation modes of the microwaves can be changed. Thus, a microwave oven that is relatively easily formed and that allows changing of the radiation modes of microwaves can be provided.
In addition, in the microwave oven according to the present invention, it is preferred that the antenna shaft is provided with a protruded portion that rotates along with the rotation of the rotational antenna, and that the antenna bearing, with the protruded portion placed on its upper end, supports the antenna shaft and presents height variation at its upper end with which the protruded portion makes contact when rotating.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.